Combustible gas is commonly ignited in gas appliances with a spark. For example, U.S. Pat. No. 4,865,539 (Geary) shows a circuit with a spark gap located in a combustion chamber into which combustible gas flows. A high voltage step up transformer has also been used to provide the operating voltage for the spark gap, and a spark gap has been used as a flame sensing mechanism. The two may be used in concert as shown in the Geary patent.
The spark generation equipment known in the art has a number of problems. Typically, a potential of 20-25 kilovolts (KV) is required to force a spark across the spark gap. This high voltage and the resulting spark generate electromagnetic interference (EMI) that sometimes causes nearby circuitry to malfunction. Recently, this problem has worsened because circuit designers are now using sensitive microcontrollers and microprocessors to implement circuit control functions in gas appliances.
Because designers commonly place circuit components in a compact area, for example, on a single printed circuit board, the high voltage step up transformer is typically located near sensitive components. Since the spark gap must be located near the gas supply, the spark gap is usually relatively far away from the other circuitry. This arrangement requires expensive high voltage wire to connect the spark gap to the remotely located control circuitry.
The high voltage wire must withstand approximately 20-25 KV to connect the step up transformer to the spark gap. Routing this high voltage wire away from sensitive components imposes design, layout, and construction constraints on the manufacturer. Furthermore, in the prior art, the spark gap and high voltage transformer are not a single unit. As a result, replacing the high voltage transformer is inconvenient and time consuming.
Accordingly, one object of the invention is to generate a spark without causing remote circuitry, including microcontrollers and microprocessors, to malfunction due to electromagnetic interference.
Another object of the invention is to reduce the need for expensive high voltage wire connecting the transformer to the spark electrodes in a spark generation apparatus.
Another object of the invention is to provide an apparatus for spark generation in which the spark electrodes and the high voltage transformer comprise a single easily replaceable module.
Still another object of the invention is to provide an apparatus for spark generation in which at least one of the spark electrodes may be used as a flame sensor.
Still another object of the invention is to provide an electronically controlled gas appliance containing an apparatus for spark generation which does not interfere with the electronic control circuitry of the appliance.
One or more of the preceding objects, or one or more other objects which will become plain upon consideration of the present specification, are satisfied by the invention described herein.